why does body temperature rise when sick
When the body temperature rises because of an infection, it's called fever. Fevers are caused by chemicals in the bloodstream called pyrogens. Pyrogens make their way to the brain's hypothalamus, which is in charge of regulating body temperature. When those pyrogens bind to certain receptors in the hypothalamus, the body temperature rises. One common pyrogen is Interleukin-1 (also called IL-1). IL-1 is produced by white blood cells that are called macrophages when they connect with certain bacteria and viruses. IL-1 has multiple purposes. An important purpose is to signal white blood cells, called helper T cells, into action. Doctors think one reason for a fever is to raise the body's temperature enough to kill off bacteria and viruses that are sensitive to temperature changes. In debate right now is whether we should be trying to lower fevers. Aspirin, for example, will reduce fever. Still, if the fever is helping rid the body of infection, then lowering it could be counterproductive.
On the other hand, people sometimes die from fever. The general medical consensus right now leans to the "reduce the fever" side of the fence.
To answer the first question, the rise in temperature has more than one benefit when our bodies are trying to fight infection. As was pointed out before, the rise in body temperature will hopefully slow down the growth of whatever bug is offending your immune system. Another point that was left out by the previous commenters involves a more complex idea that is referred to as the oxygen dissociation curve. In short, as the temperature in the body rises there are chemical changes in the red blood cell that allow it to give up more of its oxygen to the vital structures that need it during the illness. How a fever happens is a bit more complicated of an answer, but it really all boils down to (pardon that pun) your body s immune systems response to infection (or other such offense). When activated, your white blood cells are able to release a chemical called an interleukin.
There are many types of interleukins, but their main role is cell to cell communication. Certain interleukins also have the ability to interact with the hypothalamus to increase the body temperature. When this happens, our body has ways of increasing the core temperature. As one commenter mentioned, the act of shivering and muscle contraction is a very obvious way in which our body creates additional heat. The answer to where this energy comes from lies in understanding of the biochemistry of muscle movement. As you may be aware, there is a chemical called ATP that we use for many processes in our body. It is a major storage form for the energy that we have gained from our diet. When ATP is used, the reaction is exothermic, meaning it gives off heat. Similar to as if you were exercising, you contracting muscles give off heat. ObtuseAbstruse also mentioned brown fat and the thyroid gland. Brown fat is a form of fat that has the ability to generate body heat by basically using the energy of the ATP molecule as soon as it is created in a sort of exothermic chain reaction.
I am not aware that brown fat contributes much to fever however,especially in adults as we have mostly yellow fat. brown fat is more associated with the thermal regulation in the infant. In regards to the thyroid function up regulation, it is true the elevated levels of thyroid hormone will increase the metabolism and leave a person feeling hot or flushed, it is not the cause of the rise in temperature when you are ill. I hope you will appreciate the simplicity of this answer, I m sure if you are curious there is much more to discuss about the regulation of body temperature during illness. Those are just the basics that I could remember tonight. In addition, there is also room discuss the topic of inflammatory cascade products and their effects on body temperature, but I think this is enough for now.
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